Flexible display device

ABSTRACT

A flexible display device of which esthetic appearance is improved by reducing a bezel is disclosed. The flexible display device comprises a substrate including a display area and a non-display area including a bending area; a link line in the non-display area on the substrate; and a bending connection line in the bending area pf the substrate and connected with the link line, and the bending connection line located between a first buffer layer and a second buffer layer of the flexible display device.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/254,275 filed on Jan. 22, 2019 which is a continuation of U.S. patentapplication Ser. No. 15/147,498 filed on May 5, 2016 which claims thebenefit of Korean Patent Application No. 10-2015-0178916 filed on Dec.15, 2015, each of which is incorporated by reference in its entirety.

BACKGROUND Field of Technology

The present disclosure relates to a flexible display device.

Discussion of the Related Art

Recently, with the advancement of the information age, display devicesfor processing and displaying a large amount of information have beenrapidly developed. In response to this trend, various display deviceshave been introduced and spotlighted. Detailed examples of the displaydevices include liquid crystal display (LCD) devices, plasma displaypanel (PDP) devices, field emission display (FED) devices,electroluminescence display (ELD) devices, and organic light emittingdisplay (OLED) devices.

Among the display devices, the organic light emitting display devicebased on an organic light emitting diode has advantages in that theorganic light emitting diode provided in a display panel has highluminance and low operation voltage property. Also, since the organiclight emitting display device is a self-light emitting device that has agood contrast ratio, it is advantageous in that the organic lightemitting display device realizes an ultra-thin display. Also, theorganic light emitting display device has a response time of severalmicroseconds to easily display moving images, has no limitation in aviewing angle, and is stable even at a low temperature.

Recently, efforts for realizing a flat panel display device as aflexible display device to realize various objects such as easyportability, various types and damage avoidance have been made. Forexample, a liquid crystal display device and an organic light emittingdisplay device are arranged on a flexible substrate such as plastic,whereby a flexible liquid crystal display device and a flexible organiclight emitting display device can be manufactured.

However, to have a bending property of the flexible display device,development of a bending property of inner elements of the displaydevice in addition to the flexible substrate has been required.

Also, in accordance with the application of a flexible property to thedisplay device, a bezel bending technique has been introduced, whichminimizes a bezel width by bending an area corresponding to a bezelportion where image is not displayed.

FIG. 1 is a plane view illustrating a conventional flexible displaydevice based on bezel bending, FIG. 2 is an enlarged view illustratingan area A of FIG. 1, FIG. 3 is a cross-sectional view taken along lineI-I′ shown in FIG. 1, and FIG. 4 is a cross-sectional view illustratingthat a bending area of FIG. 3 is bent.

Referring to FIGS. 1 to 4, the conventional flexible display devicebased on bezel bending includes a display area 1, a non-display area 2,a bending area 3, a gate-in-panel (GIP) area 4, and a driving portion 5.

The display area 1 is an area where an image is displayed, and thenon-display area 2 is an area where an image is not displayed. A part ofthe non-display area 2 includes the bending area 3 of a bent type. TheGIP area 4 is an area where a gate driving circuit is arranged inside adisplay panel where a thin-film transistor (TFT) substrate is formed.

The display area 1 and the non-display area 2 include a substrate 25, apolyimide layer 24, a multi-barrier layer 23, an inorganic layer 22, agate insulating layer 12, a dielectric inter-layer 21, and a passivationlayer 20.

In this case, a thin film transistor layer T, a planarization layer 30,an anode electrode 40 and an auxiliary electrode 50 are formed on thedisplay area 1. The thin film transistor layer T includes an activelayer 11, a gate insulating film 12, a gate electrode 13, a dielectricinter-layer 14, a source electrode 15, and a drain electrode 16.

A bank 60 is formed on the anode electrode 40 and the auxiliaryelectrode 50 to define a pixel area, an organic light emitting layer 70is formed in the pixel area defined by the bank 60, and a cathodeelectrode 80 is formed on the organic light emitting layer 70.

In the aforementioned conventional flexible display device, as shown inFIG. 4, the bending area 4 is bent to minimize a bezel corresponding toa part of the non-display area 2. At this time, a crack may occur in asource electrode 15 connected from the thin film transistor layer T.Therefore, the conventional flexible display device uses a line havingthe same shape as a pattern of FIG. 2 to reduce such a crack.

However, in this case, the source electrode 15 is not disposed on aneutral plane, whereby the crack occurring in the source electrode 15 isnot avoided fully.

Also, in this case, a problem occurs in that it is impossible to applythe line of FIG. 2 to a high resolution display device due to a distanceP between lines and a width L of the lines as shown in FIG. 2. This isbecause there is restriction in design of the line due to an areareserved by the distance P and width L of the lines relatively increasedin the high resolution display device.

SUMMARY

Accordingly, the present disclosure is directed to a flexible displaydevice that substantially obviates one or more problems due tolimitations and disadvantages of the related art.

An advantage of the present disclosure is to provide a flexible displaydevice that can prevent a crack from occurring in lines of a bendingarea.

Another advantage of the present disclosure is to provide a flexibledisplay device of high resolution by using a straight line.

Other advantage of the present disclosure is to provide a flexibledisplay device of which esthetic appearance is improved by minimizing abezel of a non-display area.

Additional advantages and features of the invention will be set forth inpart in the description which follows and in part will become apparentto those having ordinary skill in the art upon examination of thefollowing or may be learned from practice of the invention. Theobjectives and other advantages of the invention may be realized andattained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

To achieve these objects and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein, inone embodiment a flexible display device comprises a substrate includinga display area that displays images and a non-display area where imagesare not displayed, the non-display area including a bending area wherethe flexible display device is capable of being bent; a link line in thenon-display area on the substrate; a first buffer layer in the bendingarea on the substrate; a bending connection line on the first bufferlayer in the bending area on the substrate, the bending connection lineconnected with the link line in the bending area; and a second bufferlayer on the bending connection line in the bending area of thesubstrate.

In another embodiment, a flexible display device comprises a substrateincluding a display area that displays images and a non-display areawhere images are not displayed, the non-display area including a bendingarea where the flexible display device is capable of being bent; athin-film-transistor (TFT) in the display area, the TFT including anelectrode located in a first layer of the flexible display device; abending connection line in the bending area of the non-display area, thebending connection line located in a second layer of the flexibledisplay device that is beneath the first layer that includes theelectrode of the TFT; a link line in the non-display area thatelectrically connects together the electrode of the TFT in the firstlayer and the bending connection line located in the second layer via atleast one contact hole; and a first buffer layer and a second bufferlayer, the bending connection line between the first buffer layer andthe second buffer layer in the bending area.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 is a front view illustrating a conventional flexible displaydevice;

FIG. 2 is an enlarged view illustrating an area A of FIG. 1;

FIG. 3 is a cross-sectional view taken along line I-I′ shown in FIG. 1;

FIG. 4 is a cross-sectional view illustrating that a conventionalflexible display device is bent;

FIG. 5 is a front view illustrating that a flexible display deviceaccording to the present disclosure;

FIG. 6 is a cross-sectional view taken along line II-II′ shown in FIG. 5according to one embodiment of the present disclosure;

FIG. 7 is a cross-sectional view taken along line II-II′ shown in FIG. 5according to another embodiment of the present disclosure;

FIG. 8 is a view illustrating a neutral plane of a flexible displaydevice according to the present disclosure;

FIGS. 9A to 9C are views illustrating an experiment for determining athickness of a flexible display device according to the presentdisclosure; and

FIG. 10 is a cross-sectional view illustrating that a flexible displaydevice according to the present disclosure is bent.

DETAILED DESCRIPTION

Advantages and features of the present disclosure, and implementationmethods thereof will be clarified through following embodimentsdescribed with reference to the accompanying drawings. The presentdisclosure may, however, be embodied in different forms and should notbe construed as limited to the embodiments set forth herein. Rather,these embodiments are provided so that this disclosure will be thoroughand complete, and will fully convey the scope of the present inventionto those skilled in the art. Further, the present invention is onlydefined by scopes of claims.

A shape, a size, a ratio, an angle, and a number disclosed in thedrawings for describing embodiments of the present invention are merelyan example, and thus, the present invention is not limited to theillustrated details. Like reference numerals refer to like elementsthroughout the specification. In the following description, when thedetailed description of the relevant known function or configuration isdetermined to unnecessarily obscure the important point of the presentinvention, the detailed description will be omitted. In a case where‘comprise’, ‘have’, and ‘include’ described in the present specificationare used, another part may be added unless is used. The terms of asingular form may include plural forms unless referred to the contrary.

In construing an element, the element is construed as including an errorrange although there is no explicit description.

In description of embodiments of the present disclosure, when astructure (for example, an electrode, a line, a wiring, a layer, or acontact) is described as being formed at an upper portion/lower portionof another structure or on/under the other structure, this descriptionshould be construed as including a case where the structures contacteach other and moreover, a case where a third structure is disposedthere between.

In describing a time relationship, for example, when the temporal orderis described as ‘after˜’, ‘subsequent’, ‘next˜’, and ‘before˜’, a casewhich is not continuous may be included unless ‘just’ or ‘direct’ isused.

It will be understood that, although the terms “first”, “second”, etc.may be used herein to describe various elements, these elements shouldnot be limited by these terms. These terms are only used to distinguishone element from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement, without departing from the scope of the present invention.

Features of various embodiments of the present disclosure may bepartially or overall coupled to or combined with each other, and may bevariously inter-operated with each other and driven technically as thoseskilled in the art can sufficiently understand. The embodiments of thepresent disclosure may be carried out independently from each other, ormay be carried out together in co-dependent relationship.

Hereinafter, the preferred embodiments of the present disclsoure will bedescribed in detail with reference to the accompanying drawings.

FIG. 5 is a front view illustrating that a flexible display deviceaccording to the present invention, and FIG. 6 is a cross-sectional viewtaken along line II-II′ shown in FIG. 5.

Referring to FIGS. 5, 6 and 7, the flexible display device according tothe present disclosure includes a display area 1, a non-display area 2,a driving film 5, and a GIP area 4. The non-display area 2 includes abending area 3. First of all, the display area 1 will be described,which will be followed by the non-display area 2 and the bending area 3.

The display area 1 includes a first buffer layer 220 on a substrate 210,an inorganic layer 230, a second buffer layer 240, a multi-buffer layer250, a thin film transistor T, a passivation layer 270, a planarizationlayer 180, an anode electrode 185, an auxiliary electrode 190, a banklayer 200, an organic light emitting layer 203, and a cathode electrode207.

The substrate 210 may be a plastic film. For example, the substrate 210may be, but not limited to, a sheet or film that includes celluloseresin such as TAC (triacetyl cellulose) or DAC (diacetyl cellulose), COP(cyclo olefin polymer) such as Norbornene derivatives, COC (cyclo olefincopolymer), acrylic resin such as PMMA (polymethylmethacrylate),polyolefin such as PC (polycarbonate), PE (polyethylene) or PP(polypropylene), PVA (polyvinyl alcohol), polyester such as PES (polyether sulfone), PEEK (polyetheretherketone), PEI (polyetherimide), PEN(polyethylenenaphthalate), and PET (polyethyleneterephthalate), PI(polyimide), PSF (polysulfone), or fluoride resin.

The first buffer layer 220 is arranged on the substrate 210, and may bemade of, but not limited to, PI (polyimide). In the present disclosure,since the first buffer layer 220 is an element for constituting aneutral plane, the first buffer layer 220 will be described in moredetail in the bending area 3.

The inorganic layer 230 may be made of a material that includes an oxideand a nitride, and may be made of an inorganic material such as siliconnitride (SiNx), silicon oxide (SiOx), titanium oxide (TiOx), aluminumoxide (AlOx), Indium Gallium Oxide (IGO), Indium Zinc Oxide (IZO), andIndium Gallium Zinc Oxide (IGZO). The inorganic layer 230 may serve toprevent water from being permeated thereinto. The inorganic layer 230may be directly on the first buffer layer 220 such that the first bufferlayer 220 is directly under the inorganic layer 230.

The second buffer layer 240 is arranged above the substrate 210, and maybe made of, but not limited to, PI (polyimide). In the presentdisclosure, since the second buffer layer 240 is an element forconstituting a neutral plane, the second buffer layer 240 will bedescribed in more detail in the bending area 3.

The multi-buffer layer 250 may be made of an inorganic material thatincludes an oxide and a nitride of a metal material such as silicon Si,aluminum Al, barium Ba, molybdenum Mo, copper Cu, titanium Ti, and ZincZn. The multi-buffer layer 250 serves to prevent a material contained inthe substrate 210 from being diffused into the thin film transistor Tduring a high temperature process of manufacturing processes of the thinfilm transistor T. Also, the multi-buffer layer 250 may serve to preventexternal water or humidity from being permeated into the transparentflexible display device. Thus, the multi-buffer layer 250 has a highresistance to water than other features of the transparent flexibledisplay device such as the second buffer layer 240.

The thin film transistor T includes an active layer 110, a gateinsulating film 120, a gate electrode 130, a dielectric inter-layer 140,a source electrode 150, and a drain electrode 160.

The active layer 110 is formed on the substrate 210 to overlap the gateelectrode 130. The active layer 110 may be made of a silicon basedsemiconductor material or an oxide based semiconductor material. As itis shown in FIG. 7, a light shielding layer 284 and active buffer 290may additionally be formed between the substrate 210 and the activelayer 110. In this case, external light incident through a lower surfaceof the substrate 210 may be shielded by the light shielding layer 284,whereby the active layer 110 may be prevented from being damaged by theexternal light.

The gate insulating film 120 is formed on the active layer 110. The gateinsulating film 120 serves to insulate the active layer 110 from thegate electrode 130. The gate insulating film 120 may be made of aninorganic insulating material, for example, may be made of, but notlimited to, a silicon oxide film (SiO_(X)), a silicon nitride film(SiN_(X)), or a multi-layer of SiO_(X) and SiN_(X). The gate insulatingfilm 120 may be extended to the non-display area 2.

The gate electrode 130 is formed on the gate insulating film 120. Thegate electrode 130 is formed to overlap the active electrode 110 byinterposing the gate insulating film 120 therebetween. The gateelectrode 130 may be, but not limited to, a single layer or multi-layercomprised of any one of Mo, Al, Cr, Au, Ti, Ni, Nd and Cu or theiralloy.

The dielectric inter-layer 140 is formed on the gate electrode 130. Thedielectric inter-layer 140 may be formed of the same inorganicinsulating material as that of the gate insulating film 120, forexample, may be formed of, but not limited to, a silicon oxide film(SiO_(X)), a silicon nitride film (SiN_(X)), or a multi-layer of SiO_(X)and SiN_(X).

The source electrode 150 and the drain electrode 160 are formed on thedielectric inter-layer 140 to face each other. The aforementioned gateinsulating film 120 and the aforementioned dielectric inter-layer 140are provided with a first contact hole CH1 and a second contact holeCH2, wherein the first contact hole CH1 exposes one end area of theactive layer 110, and the second contact hole CH2 exposes the other endarea of the active layer 110. The source electrode 150 is connected withthe other end area of the active layer 110 through the second contacthole CH2, and the drain electrode 160 is connected with the one end areaof the active layer 110 through the first contact hole CH1. Also, thesource electrode 150 may be extended to the non-display area 2 and thenconnected with a first link line 151.

The aforementioned thin film transistor layer T may be modified tovarious structures known to those skilled in the art without limitationto the above structure as shown. For example, although the thin filmtransistor T is formed in a top gate structure in the drawing in whichthe gate electrode 130 is formed above the active layer 110, the thinfilm transistor T may be formed in a bottom gate structure in which thegate electrode 130 is formed below the active layer 110.

The passivation layer 270 is formed on the thin film transistor layer T,more specifically on the source electrode 150 and the drain electrode160. The passivation layer 270 serves to protect the thin filmtransistor layer T, and may be made of, but not limited to, an inorganicinsulating material, for example, SiO_(X) or SiN_(X).

The planarization layer 180 is formed on the passivation layer 270. Theplanarization layer 180 serves to planarize the upper portion of thesubstrate 210 provided with the thin film transistor layer T. Theplanarization layer 180 may be made of, but not limited to, an organicinsulating material such as acrylic resin, epoxy resin, phenolic resin,polyamide resin, and polyimide resin.

The anode electrode 185 is formed on the planarization layer 180. Theaforementioned passivation layer 270 and the aforementionedplanarization layer 180 are provided with a third contact hole CH3 thatexposes the source electrode 150, and the source electrode 150 and theanode electrode 185 are connected with each other through the thirdcontact hole CH3.

The auxiliary electrode 190 is formed on the same layer as that of theanode electrode 185. The auxiliary electrode 190 serves to reduceresistance of the cathode electrode 207 which will be described later.

The bank layer 200 is formed at one surface of the planarization layer180 and over both edges of the anode electrode 185 and both edges of theauxiliary electrode 190. The planarization layer 180 includes the thirdcontact hole CH3 that exposes the source electrode 150 from thepassivation layer 270 and the planarization layer 180. The bank layer200 may prevent water from being permeated into the transparent flexibledisplay device. The bank layer 200 may be made of, but not limited to,an organic insulating material such as polyimide resin, acrylic resin,and BCB.

Although not shown, the organic light emitting layer 203 may be formedin a structure that a hole injecting layer, a hole transporting layer,an organic light emitting layer, an electron transporting layer and anelectron injecting layer are sequentially deposited. In this case, oneor two or more of the hole injecting layer, the hole transporting layer,the electron transporting layer and the electron injecting layer may beomitted. The organic light emitting layer may be formed to emit samecolored light, for example, white color for each pixel, or may be formedto emit different colored light, for example, red, green and blue lightdifferent for each pixel.

The cathode electrode 207 is formed on the organic light emitting layer203. Since the cathode electrode 207 is formed on a surface where lightis emitted, the cathode electrode 207 is made of a transparentconductive material. Since the cathode electrode 207 is made of atransparent conductive material, it has high resistance. Therefore, toreduce resistance of the cathode electrode 207, the cathode electrode207 is connected with the auxiliary electrode 190. The cathode electrode207 may be formed through a deposition process, such as sputtering,which does not have good linearity of a deposition material.

Although not shown, an encapsulation layer may additionally be formed onthe cathode electrode 207 to prevent water permeation from occurring.Various materials known in the art may be used as the encapsulationlayer. Also, although not shown, a color filter for each pixel mayadditionally be formed on the cathode electrode 207. In this case, theorganic light emitting layer 203 may emit white light.

Next, in the GIP area 4, respective layers are formed to correspond tothe display area 1, and a plurality of driving devices and power linesare formed on the gate insulating film 120. Also, the inorganic layer230 in the GIP area 4 may be provided with a light shielding layer 282formed on the same layer as that of a bending connection line 280 by thesame process as that of the bending connection line 280 which will bedescribed later. However, without limitation to this example, the lightshielding layer 282 may be formed in any one area of the display area 1,the non-display area 2 and the GIP area 4.

Next, the driving film 5 is arranged in parallel with the non-displayarea 2 and transfers an electrical signal for displaying an image to thedisplay area. The driving film 5 is connected with a second link line153 which will be described later. That is, a circuit pad (not shown)may be formed at one end of the driving film 5 to be connected with anexternal system (not shown), whereby the display area 1 is electricallyconnected with the external system.

Next, the non-display area 2 and the bending area 3 of the flexibledisplay device according to the present disclosure will be described inmore detail. Repeated description of the display area 1 will be omitted.

The non-display area 2 and the bending area 3 of the flexible displaydevice according to the present disclosure additionally include a fourthcontact hole CH4, a fifth contact hole CH5, a bending connection line280, a first link line 151, and a second link line 153. Also, theinorganic layer 230 in the non-display area 2 may be provided with alight shielding layer formed on the same layer as that of the bendingconnection line 280 by the same process as that of the bendingconnection line 280.

The source electrode 150 of the display area is extended to the firstlink line 151, whereby the first link line 151 is electrically connectedwith one end (e.g., a first end) of the bending connection line 280 ofthe bending area through the fourth contact hole CH4. The other end(e.g., a second end) of the bending connection line 280 is connectedwith the second link line 153, which is connected with a pad portion,through the fifth contact hole CH5. Also, the link line 151 and thesecond link line 153 may be arranged in parallel with each other whilethe flexible display device is bent in the bending area as shown in FIG.9.

The inorganic layer 230 may include a first inorganic layer and a secondinorganic layer. The bending connection line 280 may be formed on thefirst inorganic layer at the bending area. And then, the secondinorganic layer may be formed on the first inorganic layer and thebending connection line 280. Therefore, the bending connection line 280is arranged to be surrounded by the inorganic layer 230.

Also, the inorganic layer 230 is disposed between the first buffer layer220 and the second buffer layer 240 such that the first buffer layer 220is directly under the inorganic layer 230 and the second buffer layer240 is directly on the inorganic layer 230.

The first buffer layer 220 and the second buffer layer 240 may be formedof a same material such as polyimide at the same thickness byinterposing the inorganic layer 230 there between. However, the firstbuffer layer 220 and the second buffer layer 240 may be made ofcellulose resin such as TAC (triacetyl cellulose) or DAC (diacetylcellulose), COP (cyclo olefin polymer) such as Norbornene derivatives,COC (cyclo olefin copolymer), acrylic resin such as PMMA(poly(methylmethacrylate), polyolefin such as PC (polycarbonate), PE(polyethylene) or PP (polypropylene), PVA (polyvinyl alcohol), PES (polyether sulfone), PEEK (polyetheretherketone), PEI (polyetherimide), PEN(polyethylenenaphthalate), and PET (polyethyleneterephthalate), etc.without limitation to polyimide.

As described above, the bending connection line 280 to which the firstand second link lines 151 and 153 are connected is arranged between thefirst and second buffer layers 220 and 240 unlike the conventionalflexible display device, whereby the high resolution flexible displaydevice having a linear line structure can be obtained.

Since the bending connection line 280 is arranged between the firstbuffer layer 220 and the second buffer layer 240, a neutral plane isformed on the bending connection line 280. The neutral plane means aplane that is only to be bent with maintaining its original lengthwithout being increased or reduced when a bending moment is appliedthereto. That is, the neutral plane means a plane that a minimum forceis applied to a bending surface by counterbalancing of a tensile stressand a compressive stress applied to the bending connection line duringbending.

Also, the neutral plane NP occurring when a bending moment is applied toan object is formed in the middle of the object. Therefore, if upper andlower portions arranged by interposing a line there between have thesame thickness and the same property as each other if possible, the lineto be protected by the neutral plane NP occurring when bending moment isapplied to the flexible display device is formed.

Hereinafter, the neutral plane formed in the first and second bufferlayers 220 and 240 and the bending connection line 280 of the flexibledisplay device according to the present disclosure will be describedwith reference to FIG. 8.

FIG. 8 is a view illustrating a neutral plane formed in a bending areaof a flexible display device without bending of the bending areaaccording to the present disclosure. The neutral plane NP is formed atthe center of the bending connection line 280 shown in FIG. 8. At thistime, a force in an arrow direction is transferred from a dotted lineshown in a vertical direction to a straight line tangent to the dottedline in a diagonal direction. In this case, upper arrows based on theneutral plane NP represent a tensile stress, and lower arrows based onthe neutral plane NP represent a compressive stress. If this tensilestress and the compressive stress are applied repeatedly or at abreaking strength or more, the line formed in the flexible displaydevice may be damaged or shorted

In this respect, in the flexible display device according to the presentdisclosure, to minimize a bezel and prevent the bending connection line280 disposed in the bending area 3 from being damaged, a thickness ofeach layer on the bending area 3 may be determined such that the neutralplane may be disposed on the bending connection line 280.

FIGS. 9A and 9B illustrate experiments for determining thicknesses of asubstrate and buffer layers of a flexible display device according tothe present disclosure. FIG. 9C illustrates that a thickness of eachlayer of the flexible display device according to the present inventionis set based on the above experiments.

Axes X of graphs in FIGS. 9A and 9B mean a distance where the neutralplane occurs, and axes Y represent stress and strain, respectively. Ananalysis method through such simulations shown in FIGS. 9A and 9B isbased on a neutral plane's theory about Young's Modulus (E), Poisson'sratio (v), thickness (d), Strain (c) and Layer Total Thickness (h).

Referring to FIGS. 9A and 9B, when a total thickness to reach thebending connection line 280 including the thickness of the substrate is60.1 μm or 60.2 μm, the neutral plane may be formed on the bendingconnection line 280. That is, if a line is arranged at a point where atotal thickness to reach the bending connection line 280 including thesubstrate is 60.1 μm or 60.2 μm, to protect the point, minimum strainacts on the point. Therefore, the bending connection line 280 isarranged using the point as a target point.

Referring to FIG. 9C, when the thickness of the substrate 210 isdesigned at 50 μm, the thickness of the first buffer layer 220 at 10 μm,the thickness of the inorganic layer 230 at 0.1 μm, the thickness of thesecond buffer layer 240 at 10 μm and the thickness of the multi-bufferlayer 250 at 1.2 μm, and the bending connection line 280 is arranged onthe inorganic layer 230, the neutral plane may be formed on the bendingconnection line 280. That is, when the thickness of each layer of theflexible display device according to the present disclosure is as shownin FIG. 9C, the neutral plane is formed on the bending connection line280, whereby the bending connection line 280 is neither damaged norshorted even in case of bending. However, the above thickness is onlyexemplary, and a position of the neutral plane may be varied dependingon thickness or property of the substrate and thickness or property ofthe first and second buffer layers 220 and 240. Therefore, a desiredneutral plane may be designed using a thickness value that may bedesigned easily by the person with ordinary skill in the art. Forexample, the first and second buffer layers 220 and 240 may be designedto have the same thickness and the same property as each other.

Also, an island pattern is formed in the bending area 3 through etchingas shown in FIG. 8. This pattern structure may reduce a concentrationlevel of stress as compared with an inorganic single layered structure,whereby occurrence of a crack may be reduced. Although one islandpattern structure is shown, the island pattern structure is not limitedto the shown structure. For example, a plurality of island patterns maybe formed through etching.

FIG. 10 is a cross-sectional view illustrating that a bending area of aflexible display device according to the present disclosure is bent.

As will be aware of it from FIG. 10, the neutral plane where acompressive stress and a tensile stress are counterbalanced is formed onthe bending connection line 280 in the bending area 3, whereby thebending connection line 280 is neither damaged nor shorted. Also, thebending connection line 280 of the flexible display device according tothe present disclosure may be used for the high resolution flexibledisplay device in which spacing between lines is reduced, by forming astraight line structure. Also, since the bezel of the flexible displaydevice corresponding to the non-display area 2 may become thin due tobending of the bending area 3, the flexible display device of whichesthetic appearance is improved may be obtained.

As described above, according to the present disclosure, the followingadvantages can be obtained.

First of all, the flexible display device that can prevent a crack fromoccurring in the lines of the bending area can be obtained.

Secondly, the flexible display device of high resolution can be obtainedby using the straight line.

Finally, the flexible display device of which esthetic appearance isimproved can be obtained by minimizing the bezel of the non-displayarea.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the inventions. Thus, itis intended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A display device comprising: a flexible substrateincluding an active area and a non-display area, the non-display areaincluding a bending area configured to be bent; a link line including afirst link line and a second link line in the non-display area; and abending connection line including a first end connected to the firstlink line and a second end connected to the second link line, thebending connection line electrically connected with the first link lineand the second link line on the flexible substrate; wherein the firstlink line is connected to the first end of the bending connection linevia a first contact hole, and wherein the second link line is connectedto the second end of the bending connection line via a second contacthole, wherein the first link line and the second link line are arrangedin parallel with each other while the display device is bent.
 2. Thedisplay device of claim 1, wherein the bending connection line isdisposed on a neutral plane.
 3. The display device of claim 1, furthercomprising: a first buffer layer and a second buffer layer in thebending area of the flexible substrate; wherein the bending connectionline is between the first buffer layer and the second buffer layer. 4.The display device of claim 3, wherein the first buffer layer and thesecond buffer layer are made of polyimide.
 5. The display device ofclaim 3, wherein the first buffer layer and the second buffer layer aremade of a same material, and the first buffer layer and the secondbuffer layer have a same thickness.
 6. The display device of claim 3,further comprising: an inorganic layer that surrounds the bendingconnection line, the inorganic layer between the first buffer layer andthe second buffer layer in the bending area of the flexible substrate.7. The display device of claim 6, wherein the first buffer layer isdirectly under the inorganic layer and the second buffer layer isdirectly on the inorganic layer.
 8. The display device of claim 1,further comprising: a driving film connected to the second link line,wherein the driving film is arranged in parallel with the flexiblesubstrate.
 9. The display device of claim 1, wherein the bendingconnection line does not extend into the display area of the substrate.10. The display device of claim 1, wherein the first link line and thesecond link line are disposed on a same layer in the non-display area.11. The display device of claim 1, further comprising: athin-film-transistor (TFT) in the active area, the TFT including anactive layer, a gate electrode, a source electrode, and a drainelectrode, wherein the bending connection line is closer to the flexiblesubstrate than the thin-film-transistor in a vertical direction.
 12. Thedisplay device of claim 1, wherein the bending connection line has astraight line structure.
 13. The display device of claim 1, wherein thefirst contact hole and the second contact hole are in the non-displayarea.